The present invention relates to a microstrip antenna and, more particularly but not exclusively, to a microstrip antenna having a hexagonal patch.
In its simplest form, a microstrip patch antenna consists of a radiating patch positioned on a dielectric substrate which overlays a ground plane. Microstrip patch antennas have been used widely as microwave circuit elements such as transmission lines, filters, resonators, and antennas. The rapid miniaturization of complex electronic circuits has vastly increased the demand for small size antennas. Hand-held computers, aerospace applications, mobile telephones, pagers and other portable wireless equipment now comprise microstrip antennas. The desirability of microstrip antennas results from their structure, particularly in view of their compactness, conformability, aerodynamic structure and general ease of fabrication.
A microstrip antenna which is used as an extension for a microstrip transmission line radiates primarily due to the fringing electromagnetic fields between the patch edge and the ground plane. It is known that providing an antenna patch which overlays a thick dielectric substrate having a low dielectric constant improves the antenna performance since this provides better efficiency, larger bandwidth and better radiation. However, such a configuration leads to a larger antenna size. In order to design a compact microstrip patch antenna, higher dielectric constants have to be used, limiting the antenna performance to a narrower bandwidth. Another method to improve the antenna performance is to introduce parasitic elements of varying size above and/or below the driven element. The addition of parasitic elements stacked above and/or below the driven element to increase the bandwidth is less desirable in some cases because of the physical structure that is required.
A known factor that influences the performance of an antenna is the structural design of the patch. The commonly known patches are generally made of a conducting material such as copper or gold, which can be structured to form different shapes. Known shapes for the radiating patch are square, rectangular, circular, triangular, and elliptical shapes. U.S. Pat. No. 6,664,926, issued on Dec. 16, 2003, discloses a compact planar antenna wherein a radiating element in the shape of a right triangle is formed on a substrate. A ground plane may be positioned on one or both sides of the substrate. In one embodiment, the radiating elements are positioned on the substrate in groups of two or more in close proximity to one another. In another embodiment, the radiating elements are arranged in an array.
Another example of a microstrip antenna is disclosed in U.S. Pat. No. 7,015,868, issued on Mar. 21, 2006. This patent discloses an antenna in which the corresponding radiative element contains at least one multilevel structure formed by a set of similar geometric patch elements (polygons or polyhedrons) electromagnetically coupled and grouped such that each of the basic component elements can be identified in the structure of the antenna. The design is such that it provides two important advantages: the antenna may operate simultaneously in several frequencies, and/or its size can be substantially reduced.
However, both patents and other known structures for patches of microstrip antenna do not provide optimum geometrical structures that allow transmission at a wide range of frequencies, while maintaining a high antenna gain level.
There is thus a widely recognized need for a compact microstrip antenna having a patch with an optimum geometrical structure which is easy to fabricate and is devoid of the above limitations.